Paper manufacture



Nov. 3, 1936. HADHELD 2,059,343

PAPER MANUFACTURE Filed July 25. 1930 atented Nov. 3, i-93fi I PAPER MANUFACTURE Frank Hadfield, Chillicothe, Ohio, assignor, by mesne assignments, to The Mead Corporation, Dayton, Ohio, a corporation of Ohio Application July 25, 1930, Serial No. 470,594

' 1 Claim. (01. 91- 68) This invention relates to the manufacture of paper, and particularly to the manufacture of coated paper.

One of the principal objects of the invention is to provide a method of preparing a coated paper having a superior surface which is suitable for oifset printing, which method is economical and effective in operation, and is simple and easily controlled.

Still another object of the invention is to provide a superior coated paper having a surface coating sized with a mixedstarch-casein size.

Another object of the invention is to provide a method of preparing a mixed starch-casein sizing solution, and of preparing a coating composition containing sucha sizing solution. v

Still another object of the invention is to provide apparatus for carrying out the above method and for forming the above product.

Other objects and advantages of the invention will be apparent from the following description, the accompanying drawing and appended clainr.

1n the drawing, in which a preferred embodiment of apparatus is illustrated, the single figure is an elevational view, partially tic and partly in section, of apparatus constructed in accordance with this invention.

' According to this invention, the uncoated paper or raw stock as received from the paper machine is given a surface coating with a coating composition containing a mixed starch-casein size. It has heretofore been quite the common practice in the coating of paper to employ casein as a size for binding the filler and other ingredientsof the coating composition effectively on .the surface of the paper sheet. It is well recognized that a highly eflective size is necessary for surface coating work-that is, a size which has more binding power than is ordinarily necessary for use in binding the fibers together in the body of the paper as formed. Especially is this so in the case of printing paper, where the mineral filler and other ingredients are apt to pick of!" or become dislodged during the printing operation. Starch of itself does not possess suflicient binding power to'hold the mineral filler effectively on the surface oi a sheet for coated paper used in high grade printing work in magazine and book grade. Casein has been considered superior to starch for coating work, because of the high binding power of casein and because casein sized coated paper is practically damp proof and therefore can be used where the humidity is high without undue cockling or curling of the sheet.

The cost of casein is relatively hi h-in fact more than double the cost of a. good quality of starch. It is therefore desirable from the economical aspect to use a cheaper size, such as starch, along-with casein; The mixing of starch f5 and casein in a coating color for the coating of portions to form a mixed starch-casein size while 15 maintaining the solution properties of the same, and to permit the incorporation of this mixed starch-casein size with a filler suspension to 7 provide a coating mixture suitable for the production-of a superior coated paper which is suf- 2o ficiently damp proof and in which the filler and other ingredients are efiectively held on the surface of the sheet for various kinds of printing, including magazine, book and ofiset printing.

Referring, to the drawing, a casein solution tank is indicated at I 0, this tank having a jacket II with suitable inlet and outlet connections l2 and I3 having therein control valves I4 and I5 respectivelyfor the introduction of steam into the jacket in order to heat the contents of the 30 tank Ill. The jacket H is also provided with inlet and outlet connections l6 and I! provided with valves l8 and I9 respectively for the introduction ofa. cooling medium such as cold water into the jacket. A central vertical shaft '20 mounted in suitable bearings carries agitating paddles 2| which cooperate with suitable baflies 22 protruding from the wall of the tank intermediatethe paddles 2| to permit an effective agitation of the contents of the tank. The upper end of the shaft 20 is provided with a bevel gear .23 meshing with a bevel pinion 24 carried on the extended end of an armature shaft of a motor 25 seating on the cover 26 of the tank.

Inthe preparation of the casein solution, the tank lil is supplied with the desired amount of cold or tepid water, generally water at a temperature about 32 F. to 80 F. being satisfactory.

A predetermine amount of casein is then added tn the tank during agitation of the contents. This prel minary treatment in cold or tepid water serves to swell the grains and makes them more receptive for the alkali which is later as a partial cooking of the outside of the granules is apt to result at higher temperatures, and a lumpy mixture may result. A solution containing from about six parts of water to one part of casein by weight up to about twelve parts of water to one of casein gives a satisfactory solution which will blend well with the starch solution which is separately prepared, while at the same time undue dilution is avoided. After the casein has been allowed to stand in the cold or tepid water for about five minutes with agitation, then an alkaline material, such as sodium carbonate, sodium hydroxide, borax, or other similar alkaline compound, is added. Sodium carbonate is preferred for this purpose, and is preferably first made up into a solution containing about three parts of water to one part of sodium carbonate by weight. Suifioient alkaline solution is added to the casein mix to effect the solution of the casein. When sodium carbonate is used, about 12% to 15% of NazCOa onthe dry weight of the casein gives satisfactory results. The mixture is then heated with agitation until solution is effected. Accurate' control of the heating, while avoiding unduly high temperatures or direct steam injection which isinjurious, is obtained by means of the heating jacket with valve controlled steam connections. The mixture is not heated above 172 F., as above this temperature the binding properties of the casein are apt to be deleteriously affected. However, below F. it is difficult and requires a long time to eiiect solution of the casein. Consequently it is preferred to heat the solution between 168 F. and 172 F., within which temperature range a satisfactory clear solution is obtained in about thirty minutes with effective agitation.

A starch solution tank 30 having an exterior jacket 3| is also provided with a central vertical shaft 32 containing suitable agitating paddles 33 cooperating with stationary baffles 34 fixed to the wall of the tank 30. The shaft 32 is provided with a bevel gear 36 meshing with a bevel pinion 31 carried by the armature shaft of a motor 38 seating on the cover 39 of the starch solution tank. Inlet and outlet connections 4|! and 4| having control valves 42 and 43 respectively are provided for introducing a cooling medium into the jacket 3| of the starch solution tank. A steam supply pipe 44 having a control valve 45 extends down into the interior of the tank 30, and opens into the interior thereof as indicated at 46 in order to introduce steam directly into the contents of the tank 30 for heating purposes, direct steam injection not being injurious to the starch.

The starch to be dissolved is added to a measured quantity of cold water with agitation. A modified or oxidized starch, or one which is rendered readily soluble and free flowing, and which forms what is termed a thin boiling solution, is used. The starch-water mixture is then heated up by the direct injection of steam to a temperature above F., preferably approaching the boiling point in order to obtain quick solution. About one part by weight of starch to three to six parts by weight of water gives a satisfactory thin boiling solution while avoiding undue dilution. Preferably about one part of starch to four parts of water by weight is used. Continuous agitation at high temperatures effects rapid dissolving of the modified starch. with certain modified viscous starches having an acid reaction, so-called acid gums. improved results are obtained by the addition to the gum of a small amount, such as about by'weight, of an alkaline material such as borax, soda ash and the like, giving a better mixing and more adhesive gum solution. This alkali is preferably added to the cold water in which the starch is to be dissolved, prior to the cooking or heating thereof.

The casein solution is then mixed with the starch solution with agitation. The casein solution can be flowed into the starch solution, or vice versa, this depending upon the relative proportions of the ingredients. Thus, when a relatively large proportion of starch is used with reference to casein, the latter is flowed into the starch solution. For this purpose, the casein tank I0 is preferably positioned at a higher elevation than the starch solution tank 30, and is provided with a bottom outlet 41 connected by a gravity feed pipe 48 having a control valve 49 with the upper portion of the starch solution tank 30. In order to avoid injuring the binding properties of the casein, particularly where using more starch than casein, the starch solution which has been previously heated up to about 200 F. or above to effect solution is then quickly cooled by introducing a cooling medium into the jacket 3|. The temperature of the starch solution is preferably brought down to approximately that of the casein solution, so that the two solutions are mixed when at approximately the same temperature. A temperature range of about 150 F. to 172 F. gives satisfactory results for the'mixing of these solutions, a temperature approaching 170 F. being preferred. The temperature is kept high enough to avoid objectionable thickening and bad blending, while at the same time the temperature is maintained below that which will injure the binding properties of the casein. It is to be noted that one solution is flowed slowly with agitation into the other solution under controlled temperature conditions,

' which is found to permit in practical operation the effective mixing of these solutions while maintaining the solution properties thereof.

Satisfactory results are secured with mixtures of various proportions when prepared in accordance with this invention. A sizing composition containing as little as 10% by weight of casein together with 90% by weight of starch has been used in actual commercial operations with very satisfactory results. The mixed starchcasein solution is then cooled further by the introduction of .cooling water into the jacket 3| preparatory to the mixing of the size solution with a water suspension of filler, particularly where fillers other than clay are used. For this purpose, branch pipes 50 and 5| having control valves 52 and 53 respectively are preferably provided for introducing a cooling medium, such as cold water, into jacket 3| of tank 30. Of course, where time and storage conditions permit, at-v mospheric cooling may be used.

"The filler suspension of the coating composition may be prepared in any conventional manner. As illustrated, a filler suspension tank 55 is, provided with a central shaft 56 carrying stirring blades 51 which cooperate with bailles 58 carried by the wall of the tank in securing an effective mixing of the filler and suspension liquid such as water which is added thereto by the pipe 60 having the control valve 6!. The agitator is driven by means of cooperating bevel gears 62 and 63 from a motor 64 seating on the cover 65 of the tank.

-A measured quantity of filler is added .to' the tank 55, and then a'proportioned quantity of water is introduced by the pipe 60 in orderto make asuspension. of the desired consistency depending on the weight or coat required. The usual fillers may be used; clay, satinwhite, blanc fixe, and carbonate illlers' are preferred tor the coating of printing paper-such as'book'or magazine paper. The starch-casein solution having been cooled down to a. temperature preferably 5 Heretoiore-it has below 140 F. by the introductionoi' cooling medium into the jacket 3| is then allowedjto flow slowly through the outlet iillcontrolled by valve 68 into"the filler suspension tank. 55, while, the

indicated at 80, may also be used depending upon the requirements ot'the installation. The starch sol'utiontank III is connected by a feed pipe 13 having control valve ll with the filler suspension tank 80. Each filler suspension tank is provided with a bottom outlet 1!. controlled by a valve II for supplying the coating mixture to the coating machine.

been the general-practice to employ a special sizing treatment for paper in order to prepare it for oflset printing, in which method of printing .the paper comes in contact with awater dampened rubber blanket. Coated 15 filler suspension isb'eing agitated. By the addipaper inayp prepared in .accordanoe with the tion of the size slowly and ate. fairly constant temperature, a satisfactory mixing of the size and filler suspension without objectionable thickpresent invention which is very satisfactory for oflsetprinting, without employing such a s cial sizing treatment. Where a coated paper to onening or coa ulation is secured. Wh Suflicient set printing is desired, the coating composition is size making and storage facilities are available, k

it is desirable to cool the sizing solution to temperatures as lowas 770 F. before introduction* .into the filler suspension,.thereby obtaining in- I creased sizing efficiency. The sizing. solution is '25 stirred during the cooling thereof.

I The proportions of mineral filler to size may required. Satisfactory results for printing paper are secured by using about 70% to 85% by weight of mineral filler to 15% to 30% by weight.

of mixed starch casein size. I Very satisfactory results have been secured in commercial operation with a coating mixture containing by weight approximately 72% to 77% of filler such 'as play, satin white, or carbonate filler, 20% to 25%v of mixed starch-casein size, the balance being alkali, foam oil and other ingredients customarily used in coating mixtures. A mixture of filler is pref-.

erably used, such as about one part by weight of satin white to three parts by weight ofa carbonate filler, such as a precipitated calcium carbonate, this finish. In order to obtain a substantially continuous operation for continuous coating work, ,a plurali ity of starch solution. tanks are provided. A s cond starch solution tank is illustrated in the accompanying drawing at 10 having a gravity feedpipe 1 l-'controlled by a valve 12 tor-the supply or t 50, casein solution from the casein tank In thereto. The .tank 10 is constructed similarly to the tank 30, .so that further detailed illustration and description is unnecessary. A considerable (plan'- "tity pi casein solution may be initially made up in t tank in and maintained at the desired temperature range by means oi the Jacket II. A

batch of. starch solution may-be made up in one 'portion from the scope or the invention prepared as outlined above, except that a coating com osition which is substantially-neutral in ree actlo is used to provide a coated paper having a Q dampened in offset printing. This neutral reac--r tion is obtained by proper control of the solution be varied depending upon the character of paper a of the se by using ammoniato ldlgsolve the casein inplace of. soda, soda ash or'borax. The excess ammonia used in effecting solution is removed during the heating oi-the material, so that substantial neutrality of: the material is obtained. A substantially neutral starch solution withi k. giving a coated paper with a high 1 n Material economy is effected Fy the use 0! the i coating composition containing a substantial pro"- casein sized coated paper, andis superior tor plates during the printing process and the surface i the \paper has better ink aflinity. The coated 'paper of the present invention is effectively damp proof.

While the forms of the invention herein described constitute preferred embodiments therechanges may befimade therein without departing which is defined oiv starch. The resulting starch caseinsized coated paper has a softer suri'ace than a of the tanks 30 or 10, whilethe casein solution is being allowed to flow slowly from the tank l0 1 gai 33:3 g into the other starch solution'tahk containing a A coatgd paper adapwd 1dr priming andxook previously prepared starch sol'ution maintained 5 m a sheet. having-a surface coat at thedesired temperature for mixing. The mix'- containing approximately to by J after agitation and cooling may then be -weight of a mineral filler including a major proflowed into the filler suspension tank 55, and a portion of carbonate flnefand a minor promp cs fresh supblybf Blanch i Water e d i tion of satin white, and a'pproximately'30% to the starch solution tank or the preparatio'not a b e ht of a mixed starchwasem Si rresh batch, while additional casein solution is 2 apgmximately starch being allowed to flow slowly from the tank Iii m v into theother starch solution tank III. Addi T FRANK HADFIELD.

for, it isto be understood .that the invention is not limited to these precise form'sp and that 

